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substance is introduced and the boiling continued. When
a steady temperature is reached, the new boiling-point is
determined ; the tube is immediately disconnected from the
flask, the flame removed, and the volume of the solvent is
read off as accurately as possible. By repeating the process,

several determina-
tions may be car-
ried out with the
same solvent and
the same material.
The weighing of
fresh solvent for
each estimation of
new portions of
substance is also
avoided. The main
precautions to be
taken are (i) to
ensure steady boil-
ing in the flask, A,
by introducing frag-
ments of porous pot,
and (2) to conduct
the boiling at such
a rate that the drops
fall slowly and re-
gularly from the
FIG. 34.                              condenser. The in-

accuracies   of  the

method arise from constant change of concentration throughout
the operation and from impurity in the solvent, the boiling-point
of which will have a tendency to rise as the distillation proceeds.

Volume of solvent.1         d.         Jlf.   Mean.

1   I  0*8109 gem. (urea)

2   1  0-8109

17*5 c.c. (alcohol)



_             Calculated for CON2H4; M=6o.
l The constants for liquids at the boiling-point (= constant divided by the specific
gravity of the solvent at the boiling-point) are as follows :
Alcohol    ......    i5'6o                Acetone    ......    22*20
Ether      .....     30*30                Chloroform     ...    26*00
Water     .....       5*40                Benzene.......    32*80